Thermionic amplifier circuits



Mar 13, 1923.. 1,M&55@

. H. n. ARNOLD.

THERMIONIC AMPLIFIER CIRCUITS,

HLED FEB. 3, 1919.

Patented Mar, ill,

N I T E it. ill

I-IARDLD ID. ARNULD, 01F MAPLEl/VOOD, Iil'lE'l/V JERSEY, l- SS'JGrNOH TO 'WEfiTERN IELJEC- TRIC COMPANY, INCORPORATED, 035 liilil fl f YORK.

a, 5C1, CQRPORATION Oil? NJE'W THERMIIEONJEC AIKUPlL-IL IER CIRCUITS.

Application filed February To all whom it may concern:

Be it known that l, HAROLD D. rtnnonn, a citizen of the United States, residing at Maplewood, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Tllfil'll'liOll'lC ilunplifier Circuits, of which the following is a full, clear, concise, and exact description.

The invention relates to repeater circuits wherein an electron-discharge device is em ployed for receiving comparatively weak incoming impulses and for transmitting them in the same form or in a modified form but with amplified energy. Such an amplifier which has a cathode, an anode and a control member usually in the form of a grid electrode, has a very high impedance between control member and cathode which are the usual. input electrodes. This impedance is of the order of 25,000 ohms or more being in the nature of a space discharge path between electrodes in. a vacuum. Preferably, the vacuum is as perfect as practicable, substantially no positive ionization taking place during the operation of the device. lln case a source of potential is employed for making the potential of the grid always negative, the input circuit impedance is of the order of infinity, for no electrons can flow from the filament to an electrode which negative, so that no current flow takes place between cathode and grid even though the latter docs respond to the incoming potential variations.

An object of the present invention is to modify the effect of this high input impedance so that it may have any desired finite value.

This is accomplished by connecting tl e incoming line to the repeater through a transformer, the secondary coil of which shunted by a high impedance preferably a resistance of the order of 500,000 ohms, and may, for instance, ran from approximately 100,000 ohms to 1,000,000 ohms, This resistance is also in shunt to the input electrodes. The impedance between the input electrodes may be made much higher than 500,000 ohms by a battery or other source which maintains the grid negative. The impedance at the secondary side of the transformer is practically that of the 500,000 ohm resistance, as the higher impedance path between the input electrodes talces Serial l lo. 2%,750.

practically no current or at least a negligible current.

By this arrangement the same amplification can be secured with amplifier tubes having different input impedances, and it is feasible to substitute one such tube for another in a given circuit arrangement.

lrlore uniform amplification may also be secured by this arrangement with varying input power. llu the use of amplifier circuits heretofore designed it has been found that there is a tendency for small input voltages to be amplified proportionately more than large input voltages, for the reason that the input impedance of the tube is greater for small voltages than for large voltages, especially when no means is employed for maintaining the control electrode negative with respect to the cathode. By the use of a shunt path of constant resistance less thanthat between the input electrodes this tendency is substantially eliminated.

Aside from the above mentioned advantages of using the shunt impedance, it has the advantage, regardless of the function of the vacuum tube or of the circuit in which it connected, of preventing singing of the repeater in case the output and input circuits thereof are coupled, either designedl v by an. inductive coupling for instance, or accidentally by reason of the proximity o l' the input and output leads of the repeater.

it further advantage inherent in the use of a high impedance shunt between the line and the repeater is that it is possible to em ploy acuum tubes having different but high impedances in the same circuit without substantially affecting the impedance of the circuit as seen from the primary side of the transformer.

This application is a i'zontinuation in part of ap ication, l ierial No. 59,210, filed l lo vemher 1015, and of application flerial l lo. 48.873, filed September 3, 1015.

For further details of the invention, ref-- erence may be made to the drawings in which the single figure illustrates diagram matically a repeater circuit embodying the invention.

Referring in detail to the figure, the in.- ceming line 1 is adapted to be traversed by wealr incoming impulses which are to be amplified by the amplifier 2, and to be sent out in amplified form upon the line 3. Preferably, there is employed the battery 4 or other source which maintains the grid negative with respect to the cathode, in which case the input impedance of the repeater is practically infinite, as described above. The line 1 is connected to the input electrodes of the repeater which, in this case, are the grid and cathode electrodes, by the re peating coil or transformer 5. In shunt to the secondary of the repeating coil 5 and also in shunt to the input electrodes is the impedance 6, which may be non-inductive as shown and in the form of a resistance of the order of 500,000 ohms. This resistance may assume any desired form; viz, it may be av wire resistance, a lavite resistance, or a piece of paper treated with india ink and sealed in a glass tube. The battery 7 in the output circuit of the repeater supplies space current through the choke coil 8 and between cathode 9 and anode 10. If desired, the output circuit of the repeater may be coupled to the line 3 by the repeating coil 11, as shown.

lVhat is claimed is:

1. The combination of a vacuum discharge repeater of the three-electrode type, an inductive coil conductively connected to the input electrodes of said repeater, and a con ductive impedance in shunt to said coil.

2. The combination of an incoming line, an electric discharge repeater of the threeelectrode type, a transformer coupling said line to said repeater, one coil. of said transformer being conductively connected to the input electrodes of said repeater, and a conductive impedance in shunt to one of the coils of said transformer.

3. The combination of an incoming line, an electric discharge repeater ot the threeelectrode type, a transformer coupling said line to said repeater, the secondary coil of said transformer being conductively connected to the input electrodes of said rcpeater, and a conductive impedance in shunt to said secondary coil.

4. The combination of a line, a vacuum tube amplifier of the three-electrode type connected thereto, said amplifier having input terminals, means for applying a steady difierence of potential between said input terminals, and a high resistance connected to said terminals.

5. The combination of a line, a vacuum tube amplifier connected thereto, said amplifier having grid and cathode electrodes,

means for applying a steady difference of potential between said electrodes, and a resistance of the order of 100,000 ohms forming a bypath between said electrodes.

6. The combination of a vacuum tube amplifier having grid and cathode electrodes, meansfor making the potential of said grid negative with respect to said cathode, and a high resistance by-path for said electrodes.

'7. The combination of a line, a vacuum tube amplifier, a transformer for connecting said line to said amplifier, a bypath between said line and said amplifier and having an impedance of the order of 500,000 ohms, and means for maintaining the impedance of said amplifier greater than that of said bypath.

8. The combination of an incoming line, a repeater having a cathode and an anode. means for supplying a space current between said electrodes, a member for controlling said space current, means tor applying a steady difference of potential between said cathode and said control member and means between said line and said repeater for making the impedance of the repeater as seen from said line, substantially of a constant value.

9. The combination of an incoming line. an amplifier having a cathode and an :IUOJlQ, means for supplying a space current between said electrodes, a grid. electrode for controlling-said space current, means for making said grid negative with respect to said cathode, and means between said line and the input electrodes for making the impedance of said amplifier as seen from said line, substantially of a constant value.

10. The combination oi an incoming line. an amplifier having a cathode and an anode, means vtor supplying a space current between said electrodes, a grid electrode for controlling said space current. means for making said grid negative with respect to said cathode, a transformer for connecting said line to said amplifier, and a high resistance in shunt to the secondary winding of said transformer and to said grid and cathode electrodes tor making the imped ance of said amplifier as seen from said line, substantially of a constant value.

11. The combination of a line. an amplifier in circuit therewith. having an input impedance at least as high as 100,000 ohms. and a shunt between said line and said amplifier having an impedance oi an order lower than that of the input impedance oi said amplifier.

12. The combination of a. line. an amplifier in circuit therewith having an input impedance which is practically infinite. and a shunt between said line and said amplifier having an impedance of the order of 500,000 ohms.

In witness whereof. I hereunto subscribe my name this 15th day of January, A. I). 1919.

HAROLD D. ARNOLD. 

